The dude in the white hat is shown in a lot of previous images with a large backpack that he doesn’t have anymore in that photo. There are tons of clear photos of the area before the explosion they are just not being shown on the regular media sites. Yes it’s a marathon and tons of people have backpack and duffels so why not show the photos so someone in the public could say “that’s the dude who bought a pressure cooker here last week” or “that’s my quiet keeps to himself neighbor” Most likely those dudes or whoever they are describing in their “we are looking for...” are already in custody and the feds are trying to find the rest of their cell and connections without alerting them to the fact that they have those guys.